The present invention relates to a tomography method by transmission X rays and an apparatus thereof, and more particularly to an X-ray tomography method and an apparatus thereof suitable for inspection and measurement of internal structure of a circuit board with multi-layer structure.
Laminography is known as technology of detecting a tomographic image in a certain aimed focal point within an object by transmission X rays in the prior art. This technology provides that two elements among three elements, an X-ray source, an object and a detector, are moved in synchronization and a tomographic image is detected.
As such technology, for example, that disclosed in Japanese patent application laid-open No. 116040/1984 is known well. This technology comprises a step of irradiating a body by a fixed radiation ray source where the body and a surface sensing the radiation rays and positioned next to the body with respect to the radiation ray source, both included within one plane, are rotated in the same direction synchronously about the first axis line and the second axis line respectively, and the first axis line and the second axis line are arranged in parallel to each other and the first axis line is transformed into the second axis line by analogous transformation in a positive ratio and the center of the radiation ray source, and the radiation ray source, the body and the sensing surface are arranged so as to remain to the exposed state by the radiation rays during the rotation; a step of transforming a plane including the section of the body into a plane including the sensing surface by analogous transformation transforming the first axis line into the second axis line; and a step where the plane forms an angle having the same value being equal to or more than 0.degree. and less than 90.degree. with respect to the axis line, and an image of at least a part of the section is formed onto the sensing surface, thereby tomography of the body is carried out along the section of the body included within one plane. To put it briefly, this technology relates to a method that an object and a film are rotated in synchronization and tomography is carried out.
In the above-mentioned prior art, however, since the film used in the detecting section, a detection image cannot be seen in real time. Also since the image is moved in parallel on the film plane, there is a problem in that even if a linear structure extending in the moving direction exists outside the focal plane, its image is not blurred but can be clearly detected.
Further in a known example disclosed in U.S. Pat. No. 4,926,452, (Japanese patent application laid-open No. 501411/1990), an electron beam is rotated and deflected thereby an X-ray source is moved in a circular pattern, and a fluorescent screen is advanced along a circular path thereby tomography is carried out.
In this technology in the prior art, since the electron beam is rotated and deflected, aberration is generated in the electron optic system and a fine electron beam cannot be obtained. Therefore a problem exists in that an X-ray source of minute focus cannot be obtained and the detection resolution is low.